PROJECT SUMMARY: Evidence suggests that the effects of trauma exposure can be transmitted across generations to shape pathways to psychological impairment in offspring, with the perinatal period identified as pivotal to these processes. Although the mechanisms and timing of these effects are not well elucidated, an emerging literature focuses on the influence of maternal posttraumatic stress (PTS) during pregnancy. PTS affects up to 40% of pregnant women, particularly those from low-income, minority populations with documented health disparities. Maternal PTS may interrupt healthy development of biological stress systems in offspring, namely the Hypothalamic-Pituitary-Adrenal (HPA) axis, a well-defined biological pathway that is modulated by environmental and genetic factors. Recent studies have begun to link maternal PTS with biobehavioral indicators of stress reactivity in offspring, and these so-called intermediate phenotypes may serve as early markers of stress-related psychopathology, which can emerge in infancy and have cascading and disabling effects across the lifespan. Epigenetic modifications, such as DNA methylation, are hypothesized to play a critical role in influencing these processes. This hypothesis builds on studies, mainly in adults, linking PTS with DNA methylation of genes implicated in HPA axis functionality and candidate gene studies showing effects of maternal trauma exposure on DNA methylation in adult offspring. Notably, pilot data from our lab link maternal PTS during pregnancy with newborn infant DNA methylation of a single gene (FKBP5) implicated in the stress response. No study has yet applied an epigenomic approach, which offers a more holistic and unbiased method of discovery, for examining intergenerational transmission of trauma. We propose an exploratory study to prospectively explore predictive relationships between maternal pregnancy PTS, genome- wide methylation patterns in offspring at birth, multi-level biobehavioral indicators of infant stress reactivity at 6 months (i.e., respiratory sinus arrhythmia, heart rate, cortisol, observed distress), during a laboratory stress challenge, and key elements of the caregiving environment (i.e. observed maternal sensitivity, family support, family stressors), which may moderate these intergenerational effects. We build from extensive pilot work in our laboratory and an established research infrastructure for recruitment and retention. This work, which aligns well with the priorities of the National Institute of Child Health and Development is essential for delineating the origins of stress-related psychopathology and informing the optimal targets and timing for effective preventative interventions.